Contact lenses have been available in many colors, for many years, in both hard, including rigid gas permeable (RGP), and soft contact lenses. Both solid-colored lenses and tinted-colored lenses have been disclosed. Such lenses may be colored by adding the colorants to the monomers used to make the lens, while the monomers are in the liquid state and before polymerization of the monomers to form the colored lens material. Solid-colored lenses typically employ pigments to color the portion of the lens covering the iris and the color masks the underlying iris pattern while the lens is worn. Of course, with such solid-colored lenses, it is usually necessary to have a transparent area over the optical zone in order for the contact-lens wearer to see at all.
Tinted contact lenses employ dyes to provide color without completely blocking the passage of light through the lens. For example, U.S. Pat. No. 4,447,474 to Neefe discloses a method of tinting specific areas of soft contact lenses by placing the dye in a dye carrier made of a porous material of the size and shape of the area to be tinted. The soft lens is placed on the dye carrier and absorbs the dye in a predetermined pattern. The acid dyes known as azo dyes may be used to practice the invention, as may the dyes known as reactive dyes and sulfur dyes. The sulfur dyes are fixed or made fast by removing the sodium sulfide that make the dye soluble. Reactive dyes require no special fixing step, only extraction of unreacted dye, as they react chemically with the lens material and are thus made permanent. The properties of dyes are well known in the art. Water-soluble dyes for tinting have been selected on the basis of their water solubility, previous FDA approval for human use, and their commercial availability as biological dyes. Care must be taken that the water-soluble dyes do not leach from the lens and stain the ocular tissue, especially during long-term contact with the eye.
A disadvantage of tinted lenses is that, although they are capable of enhancing existing eye color or changing the color of light-colored eyes, tinted lenses are not generally able to produce a fundamental color change, for example, from dark brown to light blue. Especially with darker eyes (producing a dark background to the contact lens), it is difficult to see a color change with tinted lenses. On the other hand, although opaque lenses are generally capable of causing a fundamental color change, the result tends to be an unnatural appearance unless a pattern in the opaque colorant is very artistically drawn. Moreover, a thick opaque colorant on a lens may reduce the amount of oxygen transmitted through the lens, which may be unhealthy for the cornea.
To increase the natural appearance of a colored lens, iris-patterns have been made. See, for example, U.S. Pat. No. 4,719,657 to Bawa and U.S. Pat. No. 5414477 to Jahnke. Iris-pattern lenses can be made in various ways. For example, it is known to laminate a painted or printed iris pattern inside the lens material. A designed intermittent pattern can be generated by offset pad printing. However, current printing technology has limitations in the printing of smaller dots. They are normally in the range of at least 20 to 100 .mu.m, which may adversely affect the comfort of the lens.
Another problem with solid or tinted lenses relates to the fact that soft contact lenses in contrast to hard or RGP lenses, are most commonly fitted with a diameter larger than that of the cornea. Thus, in order for the lens to be unnoticeable and remain natural in appearance, complicated and expensive fabrication steps such as masking are generally necessary to produce a configuration involving a colored iris and a concentric outer area that is not colored, so that the colored portion will not cover the sclera of the eye. An objectionable cosmetic effect for the wearer would occur if the margin of a tinted lens were conspicuous against the white sclera of the eye. Similarly, colorants must not bleed or leach from one area of the lens to another, nor must they leach into the tear fluid and thereby ultimately into the eye.
Thin-film technology has been used for a number of years to control the transmittance and/or reflectance of coated surfaces by means of interference coatings comprising a stack of thin dielectric films of alternating low and high refractive index. Known applications include, for example, light reflectors in lamps, prescription eyeglasses, and sunglasses. In sunglasses, such coatings have been used to provide a colored surface for aesthetic reasons and/or to enhance the chromaticity of certain colors, for example, greens when playing golf. By controlling the thickness and index of refraction of each film in a stack or array of thin films constituting a coating, one can tailor the reflective and transmissive characteristics of the coating.
Various classes of coatings exist based not only upon the materials used to form said coatings, but based upon spectral reflectance characteristics as well. For instance, reflective coatings have long been available which transmit in the infrared region and reflect all or most of the visible portion of the spectrum. In the lamp industry, such coatings are known generically as "cold mirrors". Alternately, coatings are also known which transmit the infrared portion of the spectrum and reflect only a fraction of the visible spectrum. These coatings are generically known as "color correcting cold mirror" coatings. Still other coatings, which reflect the infrared and transmit visible light, are known as "hot mirrors". They are used, for example, to coat lamp bulbs to conserve energy. Still other coatings such as Optivex.RTM. are commercially available for use in filters to reflect UV but transmit visible light. They are sometimes used for track lighting and in museums to prevent fading of the dyes or pigments used in paintings or other exhibits.
U.S. Pat. No. 5,574,517 to Pang et al. discloses the use of interference coating in a visual aid for individuals with red-green color blindness or color deficiency. The subject visual aid comprises a pair of optical elements, such as the lenses of a pair of eyeglasses, each element having an interference coating applied to one surface thereof. The stack is structured to give the optical elements a pre-selected spectral transmission curve with respect to eyeglasses. It also provides a multi-colored aesthetically pleasing reflective surface when viewed from the front. Pang et al. state that the optical elements may be corrective glass or plastic lenses mounted in a pair of spectacle frames, for example, ordinary glasses. Pang et al. mention that, alternately, such optical elements may take the form of contact lenses worn directly on the eye, subject to applicable health and safety requirements. Pang et al., however, disclose no embodiment for such a contact lens. Pang et al. also report that contact lenses previously sold as visual aids for color-deficient individuals, to be worn on their non-dominant eye, including the "X-Chrom" lens, did not achieved wide acceptance. Pang et al. state that the filters used in such lenses reportedly tended to reduce the number of colors that could be perceived and reduced the overall amount of light entering the eye, making them unacceptable for use in low lighting conditions, among other problems.
None of the cited references teach that a thin-film interference coating could be effectively and advantageously applied to a contact lens to cosmetically impart natural color or brightness to the iris when worn on the eye.
In view of the above, it would be desirable to develop a colored contact lens that, on the one hand, appears natural as worn on the eye, offering outstanding aesthetic beauty to the eye of the wearer and which, on the other hand, is potentially capable of producing a variety of color changes, including more fundamental color changes. For example, it would be desirable to develop a contact lens that not only is capable of enhancing the hue of a person's iris, but which is capable of satisfactorily changing the color of the eyes of the wearer, for example, from brown to blue. It would be an additional advantage if such lenses did not fully block the iris nor require the drawing of an artificial iris pattern, but were transparent to the morphology of the iris, thus allowing light to naturally reflect the background with relatively little attenuation of the iris. It would be still a further advantage if a colored soft lens could be made without always requiring the separation of the color-imparting portion of the lens from the outer concentric portion of the lens, without resulting in unacceptable coloring of the sclera where the lens overlaps. It would also be desirable if such a colored lens were completely safe for the wearer, possessing a color that does not bleed or leach from the lens into the eye or from one part of the lens to another and that does not prevent or excessively hinder the passage of oxygen to the cornea. It would be desirable to develop a colored contact lens with all these desirable properties and advantages that is capable of economic manufacture.